The marketing surrounding this has been quite confused, especially as to exactly what Stadia is.
After reading that AMA the other day it seems apparent the intention of Stadia is not to provide a competitor to Microsoft Game Pass, but rather to the existing consoles. The USP is that you get a console without the initial expense, and after that it works just like a normal console: you buy games full price and the subscription is like PS+ or Xbox Gold where you get access to extra features and a drip feed of games over time. That’s what Stadia is, but I don’t think that’s been clear from the messaging.
Of course the problem with the model Google are pursuing, apart from the fact that cloud gaming might not work, is that there still is an initial upstart cost, as right now you have to spend £119 for the controller/chromecast, which is only £90 less than an Xbox One S on Amazon. When you factor in the godly internet connection you’re going to need and infinite data cap, that’s not a huge saving. Maybe when the next gen of console comes around and the prices get much higher, or if they bring the starting cost down, it will look like better value, but right now not so much.